Radiant energy receiver system



May 24, 1960 D. c. DAvls ET AL RADIANT ENERGY RECEIVER SYSTEM 3 Sheets-Sheef 2 Filed July 2, 1956 INVENToRs awavm/ 6. m//s BY 4a4 M. 20a/N May 24, 1960 D. c. DAvls ET AL 2,938,206

RADIANT ENERGY RECEIVER SYSTEM Cs/vrse 055 V/asa (4u os/r/vs V/aso) irme/Vey l z,9ss,zos 'RADIANr ENERGY RECEIVER SYSTEM Donovan C. Davis, Pasadena,

Whittier, Calif., assignors to Gillillan Bros., Inc., Los Angeles, Calif., a corporation of California Filed July Z, 1956, Ser. No. 596,131

26 Claims. (Cl. 343-113) This invention relates to direction finding receivers,

and more particularly to means for determining the angular position of a source of radiant energy.

Conventional direction finding receiver systems generally incorporate a direction nding receiver which may be mechanically and/ or electronically tuned to intercept the frequency of a radiant energy source. Such a system may also generally include a directional antenna and means to rotate it, for example, in azimuth. It is also generally necessary to employ automatic gain control in a direction finding receiver to make it sensitive both to extremely low and extremely high received signal power without saturating or burning up its receiving tubes. This is especially true in countermeasures applications. However, any directional antenna used in such an applicatiton will generally have side lobes in addition to amain or principal lobe. This means that with automatic gain control, signals received through the side lobes will have receiver output amplitudes equal to those received through the main lobe. Thus, the receiver may present false position indications of a radiant energy source.

The system of the present invention overcomes this problem and other disadvantages of the prior art by providing an auxiliary receiving channel to complement a' main receiving channel which may be conventional. The main receiving channel may comprise the conventional direction iinding receiver and a directional antenna having means to rotate it. The auxiliary receiving channel may comprise simply means to reduce the amplitude of a signal received by the main receiving channel in an amount proportional to the signal power received by the auxiliary receiving channel. This means that if an auxiliary channel antenna is provided in the auxiliary receiv- 'ing channel having a pattern identical to the main channel directional antenna, i.e. except for the directional antenna main lobe, reception through the directional antenna side lobes may be entirely suppressed.

Many times it may be impractical to design an auxiliary channel antenna to have a pattern substantially identical with the directional antenna except for its main lobe. However, in accordance with the invention, an omnidirectional antenna is usefully employed. In this case, the respective gains of the main and auxiliary receiving channels are adjusted in such a manner as to suppress the directional antenna side lobes. Eiective or overall gain of the main receiving channel in the direction of the main lobe is reduced in this case, but side lobe suppression s electively produced.

According to a feature of the invention automatic gain control (AGC) or instantaneous automatic gain control (IAGC) is accomplished simultaneously with side lobe suppression. In this embodiment of the invention, an auxiliary channel amplier is provided in the auxiliary receiving channel and a main channel amplifier is provided in the main receiving channel. Preferably a delay device is connected in the main receiving channel ahead ofthe main channel amplifier to eect IAGC. An-IAGC and Paul M. Brown, East' 2,938,206 Patented MayL 24, i960 detector is then connected from the auxiliary channel amplifier to impress an inverse bias on the main channel ampliiier. Thus, instantaneous automatic gain control may be accomplished and signal received through thc side lobes of the directional antenna may be simultaneously suppressed if the gain of the auxiliary channel amplifier is adjusted to a sufficiently high value.

In order to prevent unnecessary suppression of signals of low power received through the main lobe of the directional antenna, preferably a variable mu tube is incorporated in the main channel amplifier and the input signal versus gain characteristic of the auxiliary channel amplifier, which may be, for example, a logarithmic characteristic, is adjusted to match the variable bias versus gain characteristic of the main channel amplifier.

ln another embodiment of the invention, substantially vconstant gain amplifiers maybe used in both the main subtracted to suppress all video received through the side lobes of the directional antenna.

As stated previously, although an omni-directional? auxiliary channel antenna may be effectively employed to suppress side lobe video, this method of side lobe; suppression is accompanied by a reduction insensitivity to signals received through the main lobe of the main channel antenna. In accordance with one aspect of the invention, the side lobes of the directional antenna are suppressed without a substantial reduction in the sensitivity of the main receiving channel to such signals. This is accomplished by employing an auxiliary channel antenna having a cardioid type of pattern with its symmetrical axis in line with the axis of the main lobe of the directional antenna. Thus, if the cusp of the cardioid pattern is positioned at the main lobe of the directional antenna, no substantial reduction in receiver sensitivity to signals received in the direction of the main lobe will result.

it is therefore an object of the invention to provide means to suppress signals received through the side lobes of a directional antenna. v

lt is another object of the invention to provide means to suppress signals received through the side lobes of "a directional antenna in a direction iinding receiver system utilizing automatic gain control. v

'it is still another object of the invention to provide means both to suppress signals received through the side lobes ofthe directional antenna and to provide automatic gain control in a direction finding receiver system employing the directional antenna.

It is a further object of the inventionrto provide means both to suppress signals received through the side lobes of a directional antenna without reducing receiver sensitivity and, simultaneously, to provide instantaneous automatic gain control in a direction iinding receiver system employing the directional antenna.

The novel features which are believed to be characteristic of the invention, both as to its organization and method ofv operation, together with further objects and advantages thereof, will be better understood from the following description considered in connection with the accompanying drawings. It is to be expressly understood, however, that vthe drawings are for the purpose of illustration and description only and are not intended as a definition of the limits of the invention.

Fig. 1 is a block diagram of one embodiment of the invention; l Figs. 2. and 3 are graphs ofantenua patterns typical of the antennas 4ernployetlin each of the main and auxiliary receiving Ychannels shown in Fig. 1;

Fig. 4 is a diagram of .a preferred antenna pattern for an auxiliary channel antenna shown in Fig. 1; t y5 is 'a schematic vdiagram of the antennas, `reflectors,VV `and patterns produced lthereby according to a preferred embodiment ofthe invention; and

JvFig. '6 isa'block diagram of still another embodiment e of the invention.

Infthe drawings, in Fig. `l -main and auxiliary receiving channels and l2-are shown. The main receiving channelel comprises a mainchannel antenna 14 which isa-directional antenna,.a `ma in channel prcselector 16,

Va main channel mixer 18, ari auxiliary channel intermediate frequency (L -F.) amplifier 20, a delay device 42 2, a main channel IAGC amplifier 24, and a mainA channel detector 5126.

' The auxiliary receiving ehannel-lZ is similarly 'providedy with an auxiliary channel antenna 2 8 which mayhave an antenna pattern as will be vdescribed hereinafter, an

auxiliary channel preselector A30, an auxiliary channel mixer 32, anv auxiliary channel 4I.F. amplifier 34, and an AGC :detector 36, the output of which is employed to impress a negative `bias on the -main channel lAGC AVampliier 24.

"u AA'fr'equency s canmotor38 is employed to mechanically tune the main and auxiliary channel preselectors 16 v.and 30. The frequency `scan'motor'is also employed 'to `,mechanically tune a local oscillator r40, the output vof which is impressed upon main and auxiliary channel mixers -18 and 32.

Preferably an antenna drive mechanism 42 1s provided rto rotate both the main and auxiliary channels 14 and 28 synchronously. This is due to the preferred antenna pattern which may be employed for the auxiliaryrchannel antenna 28.

` Before explaining thefunction of the invention as shown in Fig. 1, 'it will be desirable to examine more closely the patterns of themain and auxiliary channel antennas 1 4 an d 28.` The auxiliary channel antenna 28 may bean omni-directional antenna and have a pattern couldbe subtracted tdminimize the etectsof signals received through the side lobes of the main channel antenna 14.

Alternatively, the .gain ofthe auxiliary receiving channel 12 may be increasedto makethe effective antenna patterns of each of the receiving channels 10 and 12 to be as indicated, at 44 and v 46 in Fig. l3.

' It is to be noted that the pattern 44 of the auxiliary channel antenna 28 loverlaps Vat least a portion of the main lobe 48 of the main channel antenna in Veither Fig. 3 or Fig.v 4. If any subtraction is made between the output signals of the main and auxiliary receiving channels 10 vo`r 12, `or .if thegain of .the main channel is made an inverse function of themagnitude ofsignals received through the auxiliary c hann'el'28, theetfective gain of Vt-he main receiving channell will bereduced inthe t direction Aof the main lobe 48 ,or the'lmain vchannel nna 1,4. For this reason, an auxiliary channelantenna pattern 52, as shown in Fig. 4, is'preferred. This is alcardioid type pattern and may be produced in a number of ways,

forexamp le, with a small reflector 5 4 shown schematically in Fig. 5. `A parabolic disc reector-S mayfalso `be employed Vwith vthe mainY channeliantenna 14 as thereshown with the auxiliaryv channel antenna 28.k f

AsV stated previously, theantenna `drive mechanism 42 is employed to rotate the main channel antennaff14-.t'o

csqh '.iforizsayrcesspf. radiant ...enersy- ,A1.t1,10ngh,v it is unnecessary to employ the frequency scan motor 38 .and .the local voscillator 40 withthe main and auxiliary channel mixers 32 to determine the frequency of a radiating source, in countermeasures applications this is also desirable. What is most important is the fact that when the auxiliary channel antenna 28 has an omni-directional pattern such as the pattern 4 4shown -in Figs. 2 and 3, the auxiliarychannel antenna A2 8 need not be rotated synchronously with the main channel antenna '14. However, rvwhen the auxiliary ,channel antenna 28 has the Yp 'at'tern 52, l the fact that; it is' nnsymmetrical means that in order to accomplish thepurpose for which the .particular Vshape of the pattern 52'was designed, the main and the side'lobes'50ofthemainfchannel,antenna 14 may 'be suppressed' 'In the operationof the direction iindingreceiver system shown lin'lfig. ,1, thejfrequencyscan motor 38,' by tuning-both the main and `auxiliary channel preselectors -16 and 3U and varying the local/ oscillator inputs to the fmain and auxiliary channel'r'nixers" 18` and 32, willcause each channel'toscana selected frequency band to deterfmine -atwhat'frequen'cy an external source, if any, is

radiating-wave energy.' The outputs of the main and auxiliary channelrnixers 18`and 32 are amplified respec -tively by tli'mainadvauxiliary channel L-F. amplifiers 20and 34 respectively. The output of the auxiliary lcharniel VI.-1`.' am1:lifier 34 is detected by the IAGC de tector V36 which impressies an inverse or negative bias on the main channelIAGCY amplier 24. The delay device 22is insertedbetvve'en themain channel LPF. amplifier 20and the, rnain channel IAGC amplifier 24 to provide 'a small necessary electronic delay for the IAGC voltage produced by ,the IAGCL detector 36 to control the Again. ofthe main channel IAGCamplier 24. Preferably the main channel IAGC amplifier 24 includes a variable Inn tube, ire.l Aa tube having a variable bias versus gain characteristic. Preferablyfthe auxiliary channel I.F. amplifier 34 has ha `logarithmic input versus gain characteristic and is provided with operating voltages and currents ,such thatthis. charaeteristic matches the variable bias versus gain characteristic of the main channelIAGC amplitierl 2 4. ythe vvgain ofthe main channelIAGC amplifier :2 4 may be a .linear function of the'stren'gth of input signals received throughthe auxiliary channel antenna 2 8.y Then, if the. gain of the auxiliary receiving channel/121s adjusted to an appropriate value, the IAGC biasfdeveloped bythefIAGC detector 36may be suflciently high to suppressany signals received in thedirecv tion of thelsideflob'es of themain channel`- -antenna 14.

Anna, driyemechanism 42l is employed to @filme rotatemthegmainand auxiliaryfchannel antennas 14 and 2 8 synehrolr'ronsly n and theja'uxiliary channel antennaf'28 has'the'p'attern152 as illustrated in Fig. 4,`it will be seen that side lobe suppression may A bea ccompl-ished without lSSlofr/gain rirl the mainrreceiving channel4 10. The main channel detector 2f6then ydetects the output of the main Aeh'arinel, IAGC amplii'erf24 Y,to produce main channel *.vvhichmayy be' utilijzed V inseveral ways, 4e.g{'it may be incorporated in'xsoni'e; ftypefof visual display.`

. VIt, is toibejnoted that, .stated previously, Van instantaneous, anto'mat'ic gaincontrol in addition 'to the suppression of -the sid'ezlobes of the main channel antenna 1,4 is itected by the nse of the system shown in Fig". 1. gain control -isfetected through the use of-the channel `I )frGC an-ip liner- 24 in accordancewith the .nl eeni'tadof thesignals received through .the-,auxiliary of a radiating source with respect to the axis of the auxiliary channel antenna 28.

Before leaving Fig. 1, it may be pertinent to note that ideally, the auxiliary channel antenna 28 should have a waveform exactly identical with all the side lobes 50 of the main channel antenna 14, but having zero gain in the direction of the main lobe 48. Structure to accomplish this purpose would be, of course, difiicult if not impossible to design. Hence, if the gain of the auxiliary channel antenna 28 is zero through the angle 9 of the main lobe 48, the necessary function of the auxiliary channel antenna 28 is performed effectively. In order to accomplish this any number of refiectors similar to the reiiector 54 shown in Fig. 5 may be employed with appropriate size, configuration and spacing from not only the auxiliary channel antenna 28 but also from the reliector 56 of the main channel antenna 14.

`As stated previously,ithe antenna drive mechanism 42 need -not be employed to rotate the auxiliary channel antenna 28 at all. This situationV is diagrammatically expressed in Fig. 6 where the auxiliary channel antenna 28 is not connected to the antenna 'drive mechanism 42;. The main and auxiliary receiving channels 110 and 12- have been somewhat modified for the embodiment of the invention shown in Fig. 6. The main receiving channel 10 in this embodiment of the invention comprises a main channel receiving assembly 60, a first main channel amplifier 62, a delay device 64, a second main channel amplifier 66, and a main channel detector 68. The auxiliary receiving channel comprises an auxiliary channel receiving assembly 70, a first auxiliary channel amplifier 72, a delay device 74, a second auxiliary channel amplifier 76, and an auxiliary channel detector 78. An IAGC detector 80 is also incorporated in the auxiliary receiving channel 12 to impress an IAGC bias similar to the bias supplied by the IAGC detector 36 shown in Fig. 1 on not only the second main channel amplifier 66 but also upon the second auxiliary channel amplifier 76. The delay devices 64 and 74 in each of the main and auxiliary receiving channels 10 and 12 are employed to delay the outputs of the first main and auxiliary channel amplifiers 62 and 72 a sufficient length of time t0 permit the bias output of IAGC detector 80 to control the outputs of second main and auxiliary channel amplifiers 66 and 76 inversely according to the amplitude of signals received through the auxiliary channel antenna 28.

The main channel detector 68 is .preferably a positive video detector and the auxiliary channel detectol 78 is preferably a negative video detector. Hence, with the use of the main and auxiliary channel detectors 68 and 78, an adder 82 may be employed to add the outputs thereof to perform an effective subtraction of the signals from each of the main and auxiliary receiving channels 10 and 12. A negative clamp 84 may be connected from the output of the adder 82 to clamp the negative video signals from the auxiliary channel detector 78 exceeding the positive video signals from the main channel detector 68 to zero or ground. The output of the negative clamp 68 thus is positive center lobe video of the main channel antenna 28, which may be employed in any desired manner. However, it will be obvious that a negative voltage, when applied to the intensity grid ofa cathode-ray tube indicator could do no damage. Hence, for many applications the clamp 84 may be unnecessary.

It will be obvious to those skilled in the art that many other changes and modifications of the invention may be made without departing from the true scope thereof as defined in the appended claims.

What is claimed is:

l. A system for determining the angular position of a source of radiant energy, said system comprising: main and auxiliary receiving channels, a directional antenna in said main receiving channel having a relatively high gain in atleast one lobe, a first delay device in said mainteassfaca -ceiving channel lfor delaying signals receivedJ through' said directional antenna, a mainchannel amplifier in said main receiving channel for amplifying said delayed signals, an auxiliary channel amplifier in said auxiliary receiving channel, and gain control means in said auxiliary receiving channel responsivevto. signals received by said auxiliary channel antenna for decreasing the effective gain of signals amplified by said main channel amplifier.

2. The invention as defined' inv claim 1, wherein saidV gain control means includes a first auxiliary channel am plifier and an instantaneous automatic gain control de-v tector responsive to the output of said first auxiliary chan nel amplifier for impressing an inverse instantaneous au tornatic gain control bias on said main channel amplifier.

3. The invention as defined in claim 2, wherein said main channel amplifier has a variable bias versus gain characteristic, and said first auxiliary channel amplifier has an input signal versus gain characteristic matched with the variable bias versus gain characteristic of said main channel amplifier to reduce the outputof said main channel amplifier substantially to zero for signals received in a direction other than that ofthe main lobe of said main channel antenna.

4. The invention as defined in claim 2, wherein a second delay device is connected from said first auxiliary channel amplifier and a second auxiliary channel amplifier is connected from said second delay device, the output of said instantaneous automatic gain control detector also being impressed uponsaid second auxiliary channel amplifier, and wherein additional means are provided to subtract the outputs of said receiving channels.

5.` A system for determining the angular position of a source o'f radiant energy, said system comprising: main andI auxiliary receiving channels, a directional antenna in said main receiving channel having a relatively high gain in at least one lobe, a first delay device in said main receiving channel yfor delayingy signals received through said directional antenna, a main channel amplifier in said main receiving channel for amplifying said delayed signals, a first auxiliary channel amplifier in said auxiliary receiving channel, an instantaneous automatic gain control detector responsive to the output of said first auxiiiary channel amplifier for impressing an instantaneous automatic gain control bias on said main channel amplifier, a second delay device connected from said first auxiliary channel amplifier, a second auxiliary channel amplifier connected from said second delay device, the Voutput of said instantaneous automatic gain control detector also being impressed upon said second auxiliary channel amplifier, a negative video detector co'nnected from said second auxiliary channel amplifier, a positive video detector connected from said main channel amplifier, and means for adding the outputs of said video detectors.

6. A system for determining the angular position of a source of radiant energy, said system comprising: main and auxiliary receiving channels, a directional antenna in said main receiving channel having a relatively high gain in at least one lobe, an auxiliary channel antenna in said auxiliary receiving channel having a gain in the direction of said one lobe at least no larger than its gain in any other direction, and means in said auxiliary receiving channel responsive to the amplitude of a signal received through said auxiliary channel antenna for'reducing proportio'nately the output signal amplitude of said main receiving channel.

7. The invention as defined in claim 6, wherein means are additionally provided to rotate at least said main channel antenna.

8. The invention as defined in claim 6, wherein the gain of said auxiliary channel antenna in the direction of said one lobe is less than its gain in any other direction.

9. The invention as defined in claim 8, wherein meana are additionally provided to rotate bo'th said main and auxiliary channel antennas synchronously. n

10. A system for determining the angular position of a andaxiliarvreeiviszchah said main eceiving'channefha ng .a relatiffely higli gain in at least' oneflobe'," first delayljdevicein said main receiving channel -for delaying signals received through said directional antenna, 'a rnain channel amplifier in said main receiving channel for amplifying said delayed signals, a first auxiliary channel amplifier in said auxiliary receiving channel, an auxiliary channel antenna in said auxiliary receiving channel having a gain inthe direction of said one lobe at least nolarger'than its gain'in any other` direction, and an instantaneous'automatic gain control detector responsive to the output loffsaid first auxiliary channel amplifier flor introducingan Vinverse instantaneous automatic'g'ain controlf bias on said main channel amplifier.

1l.v The invention as defined in claim l0, wherein means are additionally provided to' rotate at least'said main channel antennas.

l2. The inventionas dened in claim 10, wherein the gain of'said auxiliary channel antenna in the direction of said one lobe is less than itsgain in'an'y other direction.

l3. The inventionr as defined' in claim V12, wherein means are additionally Vprovided to rotate bo'th `rsaid main and auxiliary channel antennas synchronously.

14. A system for determining the angillar'position of a source of radiant energy, ',saidv`system`cnprising: main and auxiliary receiving channels, adirectional antenna in'said main receivingchannel having a relativelyhigh gain in at least one lobefa'n auxiliary channel antenna in said auxiliary receiving channel having a gainv in a direction of said one lobe less than` its gainin Aany other` direction, means to rotate both said main and auxiliary channel antennas synchronously, a first delay device in said main receiving channel for .delaying lsignals received through said directional antenna, y main channel amplifierni'n said main receiving channel for amplifying said delayedsignals, an auxiliary channel amplifier in said auxiliary receiving channel, and an instantaneous automatic gain control detector responsive to the output of said auxiliary channel amplifier f or impressing a negative instantaneous automatic gain control bias on said main channel amplifier, said main channel amplifier having a variable bias versus gain characteristic, said auxiliary channel amplifier having an input signal versus gain characteristic matched with the variable bias versus gain characteristic of said main channel amplifier to reduce ,the output of said main channel amplifier substantially to zero for signals received in a direction other than that of the main lobe of said main channel antenna.

15. A system for determining the angular position of a source of radiant energy, said Vsystem comprising: main and auxiliary, receiving channels, a directional antenna in said main `receiving channel having a relatively high gain in at least one lobe, a first delay device in said main receiving channel for delaying signals receivedv through said directional antenna, a main channel amplifier in said main receiving channel for amplifying said delayed signals, a first auxiliary channel amplifier in said auxiliary receiving channel, an instantaneous automatic gain control detector responsive Yto Athe output of said rst auxiliary channel amplifierfor impressing a negative instantaneous automatic 'gain control `bias onsaid'niain channel amplifier, a second delay device .connected'irom'fsaid,first auxiliary channel amplifier, a second auxilia'rychannel amplifier connected from said 'delay'devica the output of said instantaneous automatic gaincontrol detector also being impressedupon 1said `second auxiliary channel amplifier, and means to' subtract the outputs of said receiving channels.

16. The invention Vas definedin claim 1,5, wherein said means for subtracting the'outputs of saidreceiving channels comprise: a negative video detector connected from Said .second availiaryphaeael .amplisr ,a .essere vides detectorconnected from said main channel amplifier, and ineens to :add` the `out`p1`1`ts ft said videodeteA "trsfy 1,7. A system for determining tlieang'iilar `position of a source o'fadiantfenerg'y, said system comprising: main and auxiliaryTrecivingchannels;` a.' directional antennain said main channel havinga relatively high gain in at least one lobej an'auxiliary channel antenna in said auxiliary receiving channel having ya gain Vin the direction of said one lobe less thaniits gain inany other direction; and means in said auxiliary receiving channel responsive to the amplitude of a signal Vreceived through said auxiliary channel antenna for reducing proportionately the output signal amplitude of said" main receiving channel.

18. The invention as delined in claim 17, wherein means are additionally provided tov rotate both said main and auxiliary channel antennas at the' same angular rate;

19. The invention as defined in claim 18, wherein the pattern of said auxiliary channel antenna is cardioid in shape.

20. A system lfor determining the angular position of a source of radiant energy, said system comprising: main and auxiliary receiving channels; a directional antenna in said main receiving channel having a single main lobe of a relatively high gain and a plurality of side lobes of lower corresponding gains; an auxiliary channel antenna in said auxiliary receiving channel having a gain in the direction of all of said side lobes as large as that of said directional antenna in the direction of said side lobes; and means in said auxiliary receiving channel responsive to the amplitude of a signal received through said auxiliary channely antenna for reducing proportionately the output signal amplitude of said main receiving channel.

21. A system for determining the angular position of a source of radiantenergy, said system comprising: main and auxiliary receiving channels; a directional antenna in said main receiving channel having'a single relatively high gain main lobe aand a plurality of side lobes; an auxiliary channel antenna in said auxiliary receiving channel having a substantial gain in -the direction of said side lobes; a auxiliary channel amplifier in said auxiliary receiving channel for amplifying signals received by said auxiliary channel antenna; and a variable gain amplifier in said main receiving channel responsive to the Voutput of said auxiliary 'channel amplifier for amplifying signals received by said directional antenna, the gain of said variable gain amplifier beingreduced in proportion to signal strength in said auxiliary receiving channel, whereby side lobes of said directionalv antenna may be suppressed.

22. The invention as defined in claim 21, wherein said auxiliary channel amplifier has an input signal versus gain characteristic matched with the variable bias versus gain characteristic of said variable gain amplifier to reduce the output signal of said main channel amplifier substantially `to zero for signals received in a direction other than that of the main lobe ofy said directional antenna.

23. A radiant energy detection system comprising: main and auxiliary receiving' channels; a directional antenna in'said main channel having a relativelyhigh gain main lobe and relatively lowgain side lobes; an'auxiliary antenna in VsaidV auxiliary receiving channel, theratio' of the auxiliary lantenna gain in the direction of said main lobe to the auxiliary antenna gain in the direction of said side lobes being less than the ratio of said directional antenna gain in the direction of said main lobeto the directional antenna gain in the direction of said side lobes; and automatic gain control means to reduce the gain of said main channel in accordance with the output signal magnitude of said auxiliary channel.

24. The' invention as defined in claim 23, wherein the pattern of said auxiliary antenna is omnidirectional.

25. The invention as defined in claim 23, wherein the patterngofsaid auxilimvantenna is .cefdoid i Shape- 26. A radiant energy detection system comprising: output signal of said auxiliary channel is of a relatively main and auxiliary receiving channels; a directional anlarge magnitude. tenna in said main channel having a relatively high gain main lobe and relatively low gain side lobes; an auxiliary References Ce fl the le 0f this P211tent antenna in said auxiliary receiving channel, the ratio of 5 UNITED STATES PATENTS the auxiliary antenna gain in the direction of said main lobe to the auxiliary antenna gain in the direction of said 1)916358 Bruce July 4 1933 n,026,254 `Sandfort Dec. 31, 1935 said lobes being less than the ratio of said directional OE h N 24 1936 antenna gain in the direction of said main lobevto the di- 2661737 en anser lgv 1 1936 rectional antenna gain in the direction of said side lobes; 10 g; A551 4' 1942 and instantaneous automatic gain control means to snp 2,825,900 Coubohm Mar. 4 1958 press the output signal of said main channel when the faaea t, may 2a ieee Ta-temi Nm 3),

Donovan C; @avis et ai@ It is hereby certified that error appears in the-printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Coiumn 2I line 4?;0 ior "signa-Freed e signals my Column 3Q line 33V ier "channeis read u channel ant-@mias lime 63 eiter "channel" insert eantenna mi inline' 659 oor "or the" oi the -wg colui-'an Lv line EBU-E, ior 'radiatimgwave" radiating wave N5 Column 8 line 40 ier "a auxiliary" read an auxiliary e /7 Sigaec and this ist day oi November i960.

(SEAL) Attest:

KARL AX NE ROBERT Q WATSON Attesting Ocer Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATEl OF CORRECTION f ogg, Mey 249 i960 Donovan 6.,' Devis et aim It is hereby;r certified that error appears in the-printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2 iine iq ier "si I eed siem-ils w3 column 3v line 35% for "ehenneis reed e ehermei antennes line 63 after "chenne" ineert antenne @--g line @SQ fer or the oi the m3 column @.9 line 3%- ior "redietitigwave" reati radiating w3 column 8;, line 40, i`or+ "e auxiliary" reed am euxiiary n Signed and sealed this ist diej; ei November i960,

(SEAL) Attest:

KARL AXLENE ROBERT C. WATSON Attesting Ofcer Commissioner of Patents 

